Arachidonic acid (AA) metabolites are now known to play important roles in the functioning of normal blood vessels. AA metabolism, however leads to the production of highly reactive free radical intermediates, having the potential to inactivate AA cascade enzymes as well as damage vascular cells. AA metabolic end-products, on the other hand, specifically certain prostaglandins, may actually afford protection to cells in a number of injurious situations (cytoprotection). Factors regulating the metabolic fate of AA, especially as related to the ability of vascular tissue to withstand injurious stress are not well understood. The goal of this proposal is to study the regulation of AA metabolism in vascular tissue and to relate alterations in this process to changes in vascular integrity. These studies will be performed in intact vessels (in situ perfused rabbit aortas) and, for comparison with individual cellular elements, in cultured endothelial and smooth muscle cells. Studies on oxidative mechanisms will focus on: 1) the regulation of the entire AA cascade by oxidative metabolites of AA itself, 2) the role of these metabolites in cellular injury and cytoprotection, 3) the effects of O2 as a regulator of the AA cascade and the consequences of this interaction for cellular integrity, and 4) the effects of antioxidants. The putative increased sensitivity of endothelial cells to oxidant injury will be assessed and related to the pattern of AA metabolism in these cells. The influence of cell membrane composition, pharmacological agents, and cell-cell interactions on the oxidative mechanisms of AA cascade regulation and cellular injury will be determined. Cellular cholesterol and fatty acid content will be altered by dietary manipulation in the rabbit and by liposome incorporation in cultured cells. Drugs to be studied include those vasoactive agents known to interact with the AA cascade, especially potentially protective (nitrates, beta-blockers) or vasculotoxic (cathecholamines, angiotensin II) compounds. The potential for platelets to modulate vascular AA metabolism and susceptibility of vascular tissue to injury will be assessed. The overall objective is to understand the factors regulating AA metabolism and cellular injury in vascular tissue. These studies may provide data relevant to vascular injury in disease states such as atherosclerosis.